Nuclear magnetic resonance (NMR) is a phenomenon that a resonance occurs between a magnetic field and an atomic nucleus when a nuclear spin that is precessing in the magnetic field is applied with a rotating magnetic field having the same frequency as a Larmor frequency of the precession.
Because relaxation characteristics for the nuclear spin to return to an original state after changing the state due to the resonance are different depending on a situation of the nuclear spin, it is possible to identify a bonding structure or physical properties of an object to be measured.
More specifically, for example, an oscillating magnetic field resonating in a pulse-like manner is applied to a nuclear spin directed to be parallel or antiparallel to a magnetic field in a static magnetic field, the static magnetic field is applied in a center axis (Z axis) direction, so as to change the spin direction in an XY axis direction. After that, a period of time for the spin direction to return to the original direction (the period of time is referred to as “a relaxation time”) is measured so as to identify the bonding structure or the physical properties of the object to be measured.
Further, the relaxation time includes a vertical relaxation time T1 that is a relaxation time of a component in a center axis direction (Z axis direction) of the spin precession before the pulse is introduced, and a transverse relaxation time T2 that is a relaxation time of a component in a direction (XY axis direction) perpendicular to the center axis direction.
A measurement result of this nuclear spin relaxation state is imaged to be a magnetic resonance image (MRI). The bonding structure or the physical properties of the object to be measured are imaged based on the vertical relaxation time T1 and/or the transverse relaxation time T2.
Here, when imaging is performed based on the transverse relaxation time T2, a method of measuring T2 by Hahn echo is usually adopted (Patent Document 1).